echo '<a id="advanced_menu_toggle" href="#" '.av_icon_string('mobile_menu').'></a>';
    echo '<a id="advanced_menu_hide" href="#"   '.av_icon_string('close').'></a>';



change it to


    echo '<a title="mobile menu" id="advanced_menu_toggle" href="#" '.av_icon_string('mobile_menu').'></a>';
    echo '<a title="mobile menu" id="advanced_menu_hide" href="#"   '.av_icon_string('close').'></a>';